As a result of the development of IT technologies in recent years, there is a gradual transition of the form of administrative documents, account books and written contracts of private enterprises from conventional paper documents to electronic (digital) documents for both use and storage. More specifically, as scanners have become widely available, it is now easy to store documents as electronic data. Additionally, as high definition image scanners are being put to practical use, it is now permitted to store official documents as electronic documents instead of paper documents on condition that certain security requirements are met, although such a form of document storage was not authorized before (as a result of the enforcement of the e-Document Law in April, 2005).
On the other hand, as the demand for electronic storage of documents increases, the necessity of storing and managing electronic documents in safe becomes strong. In order to electronically store the documents that used to be stored as paper documents, maintaining the admissibility of evidence thereof, it is believed that certain technical requirements such as “detection and prevention of falsification”, “identification of document author”, “access management and control” and “history management” need to be met. Existing document management systems are functionally insufficient for satisfying these requirements and the development and marketing of “originality assurance systems” that satisfy these technical requirements is in rapid progress.
The most popularly employed security element techniques for “originality assurance system” include those of digital signature and time stamp. With the technique of digital signature, it is possible to identify the author of a document and testify and confirm that the document has not been altered (unfalsifiedness) since the time of preparation to the third party. With the technique of time stamp, it is possible to prove the established time of an electric document so that it is desirable to use such a technique in addition to providing the function of digital signature.
The conventional concept of originality assurance that can be realized by utilizing the above-described techniques is applicable to documents whose originals can clearly be located as in the case of securely managing and storing originals of established final forms as paper documents in keyed stack rooms.
In such an environment, the techniques of digital signature and time stamp are very effective for assuring the identify and unfalsifiedness of an electronic document. Known techniques for securing the originality of an electronic document include those described in Patent Documents 1 and 2 listed below and Patent Document 3 listed below describes a known technique of solving the electronic document sanitizing problem, while Non-Patent Document 4 listed below describes a known electronic document sanitizing technique of making it possible to determine if it is permissible to additionally sanitize a disclosed document or not under control.
IPSJ SIG Notes, “Digital Document Sanitizing Problem” (2003 Jul. 17) (2003-CSEC-22-009) proposes a solution system. Additionally, SCIS2004 Paper “A Digital Document Sanitizing Scheme with Disclosure Condition Control” proposes an electronic document sanitizing technique of making it possible to determine if it is permissible to additionally sanitize a disclosed document or not under control.    Patent Document 1: Japanese Laid-open Patent Publication No. 2000-285024    Patent Document 2: Japanese Laid-open Patent Publication No. 2001-117820    Non-Patent Document 3: IPSJ SIG Notes, “Digital Document Sanitizing Problem” (2003 Jul. 17) (2003-CSEC-22-009)    Non-Patent Document 4: SCIS2004 Paper “A Digital Document Sanitizing Scheme with Disclosure Condition Control”